1. Field of the Invention
The present invention relates generally to a wafer polishing apparatus, and more particularly to a wafer polishing apparatus which has a retainer ring and presses a wafer against a rotating turn table to polish the wafer whose peripheral edge is enclosed by the retainer ring.
2. Description of Related Art
Japanese Patent Provisional Publication No. 8-229808 discloses a wafer polishing apparatus which has a retainer ring enclosing the periphery of a wafer and presses the retainer ring and the wafer against a turn table to polish the wafer. The wafer polishing apparatus is provided with an annular tube which is arranged between the retainer ring and a wafer holding head. Japanese Patent Provisional Publication No. 8-229808 also discloses a method of adjusting a pressure force of the retainer ring by adjusting the air pressure within the tube, and a method of adjusting the pressure force with use of a diaphragm.
A conventional wafer polishing apparatus, however, cannot uniformly press over the circumference of the retainer ring, since the supply of the air to the tube causes a weak portion thereof to expand excessively. The irregular pressure force causes the polishing pressure against the wafer to be irregular. Thus, the wafer cannot uniformly be polished.
The method of adjusting the pressure force of the retainer ring by means of the diaphragm has a disadvantage because the movable range of the retainer ring is too narrow to obtain a necessary pressure force.